Each swimmer's leading three efforts count towards the series, with double points on offer for the final race on April 6 - the King of the Bays in Auckland.

"If I can pick up one more win, it'll all come down to the King of the Bays.

"It's going to be an interesting series," Radford said.

Webby was a surprise winner in the women's race ahead of the more fancied Cara Baker.

After the pair swam together at the start, Webby, from Taranaki, moved into overdrive at the 1000m mark and won by just over a minute.

Wellington's Courtney Carson was third, 3min 24sec behind Webby.

Webby's victory was a boost after some disappointing results at the national championships a fortnight ago, which Baker dominated. "I was lacking confidence before going out, because my last two ocean water swims haven't been great," Webby said.

The women's series is now nicely set up - Webby has won two of the three races, and Baker one. The next race is La Grande Classic at Akaroa on February 23.